Action of different types of endoxylanases on eucalyptus xylan in situ

Most studies of the mode of action of industrially important endoxylanases have been done on alkali extracted-plant xylan. In just few cases, the native form of the polysaccharide, acetylated xylan, was used as a substrate. In this work action of xylanases belonging to three glycoside hydrolase families, GH10, GH11, and GH30 was investigated on acetylglucuronoxylan directly in hardwood cell walls. Powdered eucalyptus wood was used as xylanase substrate. Enzyme-generated fragments were characterized by TLC, MALDI ToF MS, and NMR spectroscopy. All three xylanases generated from eucalyptus wood powder acetylated xylooligosaccharides. Those released by GH10 enzyme were the shortest, and those released by GH30 xylanase were of the largest diversity. For GH30 xylanase the 4-O-methyl-D-glucuronic acid (MeGlcA) side residues function as substrate specificity determinants regardless the acetylation of the neighboring hydroxyl group. Much simpler xylooligosaccharide patterns were observed when xylanases were applied in combination with carbohydrate esterase family 6 acetylxylan esterase. In the presence of the esterase, all aldouronic acids remained 3-O-acetylated on the xylopyranosyl (Xylp) residue substituted with MeGlcA. The 3-O-acetyl group, in contrast to the acetyl groups of otherwise unsubstituted Xylp residues, does not affect the mode of action of endoxylanases, but contributes to recalcitrance of the acidic xylan fragments. The results confirm importance of acetylxylan esterases in microbial degradation of acetylated hardwood glucuronoxylan. They also point to still unresolved question of efficient enzymatic removal of the 3-O-acetyl group on MeGlcA-substituted Xylp residues negatively affecting the saccharification yields.

     

Mode of Action of Clostridium Phage HM 7-Induced Lytic Enzyme on Clostridium saccharoperbutylacetonicum Cell Wall Peptidoglycan

The action of Clostridium phage HM 7-induced lytic enzyme on the cell wall peptidoglycan of Clostridium saccharoperbutylacetonicum was investigated. The cell wall peptidoglycan of this strain contained glutamic acid, alanine, diaminopimelic acid, glucosamine and muramic acid in the molar ratios of 1.00: 2.08: 0.97; 0.92: 0.68. It was strongly digested when incubated with the lytic enzyme. This digestion was accompanied by the release of NH₂-terminal l-alanine without a concomitant release of COOH-terminal amino acids and reducing groups. Chromatography of the lytic enzyme digest resulted in only two fractions, each of which was chromatographically homogeneous. One was a polysaccharide consisting of glucosamine and muramic acid in molar ratios 1.00: 0.78, and other was a peptide composed of glutamic acid, alanine and diaminopimelic acid in molar ratios of 1.00: 2.09: 1.05. These results indicate that phage HM 7-induced lytic enzyme is N-acetylmuramyl-l-alanine amidase, which cleaves the linkage between N-acetylmuramic acid and l-alanine.

A possible structure for the cell wall peptidoglycan was also proposed.     

Comparison of Sucrose-Hydrolyzing Enzymes Produced by Rhizopus oryzae and Amylomyces rouxii

Rhizopus oryzae produces lactic acid from glucose but not efficiently from sucrose, while Amylomyces rouxii, a species closely related to R. oryzae, ferments these sugars equally. The properties of two sucrose-hydrolyzing enzymes purified from culture filtrates of R. oryzae NBRC 4785 and A. rouxii CBS 438.76 were compared to assess lactic acid fermentation by the two fungi. The substrate specificity of the enzymes showed that the enzymes from strains NBRC 4785 and CBS 438.76 are to be classified as glucoamylase and invertase respectively. The entity of the enzyme from strain NBRC 4785 might be a glucoamylase, because eight residues of the N-terminal amino acid sequence coincided with those of the deduced protein from the amyB gene of R. oryzae. The enzyme from NBRC 4785 was more unstable than that from strain CBS 438.76 under conditions of lower pH and higher temperature. These observations mean that the culture conditions of R. oryzae for lactic acid production from sucrose should be strictly controlled to prevent inactivation of the glucoamylase hydrolyzing sucrose.     

Molecular Characterization of a Novel Family-46 Chitosanase from Pseudomonas sp. A-01

Pseudomonas sp. A-01, isolated as a strain with chitosan-degrading activity, produced a 28 kDa chitosanase. Following purification of the chitosanase (Cto1) and determination of its N-terminal amino acid sequence, the corresponding gene (cto1) was cloned by a reverse-genetic technique. The gene encoded a protein, composed of 266 amino acids, including a putative signal sequence (1-28), that showed an amino acid sequence similar to known family-46 chitosanases. Cto1 was successfully overproduced and was secreted by a Brevibacillus choshinensis transformant carrying the cto1 gene on expression plasmid vector pNCMO2. The purified recombinant Cto1 protein was stable at pH 5–8 and showed the best chitosan-hydrolyzing activity at pH 5. Replacement of two acidic amino acid residues, Glu23 and Asp41, which correspond to previously identified active centers in Streptomyces sp. N174 chitosanase, with Gln and Asn respectively caused a defect in the hydrolyzing activity of the enzyme.     

Analysis of muramic acid in holocene microbial environments by gas chromatography,electron impact,and fast atom bombardment mass spectrometry

Analytical procedures have been modified to determine the abundance of muramic acid in four different Holocene sediment samples. Muramic acid is specific to the peptidoglycan moiety of the cell walls of most eubacterial pro‐karyotic organisms. The following procedure seemed to be the most appropriate for the detection of muramic acid and amino acids, including diaminopimelic acid. Hydrolysis of the samples (in 6 N HCl, 4.5 h, at 100°C) was followed by separation and purification of amino sugars and amino acids using Amberlite XAD‐2 and then Bio‐Rad AG 50W‐X8 resins. The N,O‐heptafluorobutyryl‐n‐butyl ester derivatives were prepared by esterification in acidified (3 N HCl) n‐butanol for 3 h at 100°C, followed by acylation by refluxing with heptafluorobutyric anhydride in acetonitrile (2:1 v/v) for 12 min at 150°C. The derivatives were analyzed by gas chromatography (GC) and gas chromatography‐mass spectrometry. Fast atom bombardment (FAB) ionization was used for the muramic acid derivative to determine its molecular weight and structure, d‐and l‐amino acids were separated by GC and a capillary chiral column. By using this technique a stable N,O‐heptafluo‐robutyryl‐n‐butyl ester derivative of muramic acid was identified at picogram levels in Holocene sedimentary microbial communities. It has been reported previously that microorganisms in sediments rapidly degrade muramic acid from cell walls of dead prokaryotes. Kinetic experiments revealed that muramic acid was relatively stable in intact cell walls but decomposed rapidly in the free form. These investigations noted above showed that the concentration of muramic acid may be used as an indicator of the presence of the intact cell walls of cyanobacteria and most other bacteria in Holocene microbial communities, and of microbial contamination in samples older than the Holocene.     

Positional specifity of acetylxylan esterases on natural polysaccharide: An NMR study

Background

Microbial degradation of acetylated plant hemicelluloses involves besides enzymes cleaving the glycosidic linkages also deacetylating enzymes. A detailed knowledge of the mode of action of these enzymes is important in view of the development of efficient bioconversion of plant materials that did not undergo alkaline pretreatment leading to hydrolysis of ester linkages.

Methods

In this work deacetylation of hardwood acetylglucuronoxylan by acetylxylan esterases from Streptomyces lividans (carbohydrate esterase family 4) and Orpinomyces sp. (carbohydrate esterase family 6) was monitored by ¹H-NMR spectroscopy.

Results

The ¹H-NMR resonances of all acetyl groups in the polysaccharide were fully assigned. The targets of both enzymes are 2- and 3-monoacetylated xylopyranosyl residues and, in the case of the Orpinomyces sp. enzyme, also the 2,3-di-O-acetylated xylopyranosyl residues. Both enzymes do not recognize as a substrate the 3-O-acetyl group on xylopyranosyl residues α-1,2-substituted with 4-O-methyl-d-glucuronic acid.

Conclusions

The ¹H-NMR spectroscopy approach to study positional and substrate specificity of AcXEs outlined in this work appears to be a simple way to characterize catalytic properties of enzymes belonging to various CE families.

Significance

The results contribute to development of efficient and environmentally friendly procedures for enzymatic degradation of plant biomass.     

Cloning,Sequence Analysis,and Expression in Escherichia coli of the Gene Encoding Monovalent Cation-activated Levodione Reductase from Corynebacterium aquaticum M-13

The gene encoding (6R)-2,2,6-trimethyl-1,4-cyclohexanedione (levodione) reductase was cloned from the genomic DNA of the soil isolate bacterium Corynebacterium aquaticum M-13. The gene contained an open reading frame consisting of 801 nucleotides corresponding to 267 amino acid residues. The deduced amino acid sequence showed approximately 35% identity with other short chain alcohol dehydrogenase/reductase (SDR) superfamily enzymes. The probable NADH-binding site and three catalytic residues (Ser-Tyr-Lys) were conserved. The enzyme was sufficiently produced in recombinant Escherichia coli cells using an expression vector pKK223-3, and purified to homogeneity by two-column chromatography steps. The enzyme purified from E. coli catalyzed stereo- and regio-selective reduction of levodione, and was strongly activated by monovalent cations, such as K⁺, Na⁺, and NH₄ ⁺, as was the case of that from C. aquaticum M-13. To our knowledge, this is the first sequencing report of a monovalent cation-activated SDR enzyme.     

Cell wall and sheath constituents of the cyanobacterium Gloeobacter violaceus

Sheaths isolated from Gloeobacter violaceus were found to be composed of a major polysaccharide moiety (glucose, galactose, rhamnose, mannose, arabinose), a protein moiety, and negatively charged components (glucuronic acids, phosphate, sulfate). Outer membrane polypeptide patterns were dominated by two major peptidoglycan-associated proteins (M_r 62,000 and 53,000). Lipopolysaccharide constituents were glucosamine, 3-hydroxy fatty acids (3-OH-14:0, anteiso-3-OH-15:0, 3-OH-16:0, 3-OH-18:0), carbohydrates, and phosphate. A1-type peptidoglycan and non-peptidoglycan components (mannosamine, glucose, mannose, and glucosamine) indicated the presence of a peptidoglycan-polysaccharide complex in the cell walls of Gloeobacter violaceus.Abbreviations A₂pm diaminopimelic acid - ATCC American Type Culture Collection - CE cell envelope - CM cytoplasmic membrane - CW cell wall - dOcla 3-deoxy-d-manno-2-octulosonic acid - GalN galactosamine - GlcN glucosamine - GlcUA glucuronic acid - HF hydrofluoric acid - LPS lipopolysaccharide - ManN mannosamine - M relative molecular mass - MurN muramic acid - MurN-6-P muramic acid-6-phosphate - OMe O-methyl - PAGE polyacrylamide gel electrophoresis - PCC Pasteur Culture Collection - SDS sodium dodecyl sulfate - SH sheath     

Purification, characterization, and molecular cloning of organic-solvent-tolerant cholesterol esterase from cyclohexane-tolerant Burkholderia cepacia strain ST-200

Extracellular cholesterol esterase of Burkholderia cepacia strain ST-200 was purified from the culture supernatant. Its molecular mass was 37 kDa. The enzyme was stable at pH 5.5–12 and active at pH 5.5–6, showing optimal activity at pH 7.0 at 45°C. Relative to the commercially available cholesterol esterases, the purified enzyme was highly stable in the presence of various water-miscible organic solvents. The enzyme preferentially hydrolyzed long-chain fatty acid esters of cholesterol, except for that of cholesteryl palmitate. The enzyme exhibited lipolytic activity toward various p-nitrophenyl esters. The hydrolysis rate of p-nitrophenyl caprylate was enhanced 3.5- to 7.2-fold in the presence of 5–20% (vol/vol) water-miscible organic solvents relative to that in the absence of organic solvents. The structural gene encoding the cholesterol esterase was cloned and sequenced. The primary translation product was predicted to be 365 amino acid residues. The mature product is composed of 325 amino acid residues. The amino acid sequence of the product showed the highest similarity to the lipase LipA (87%) from B. cepacia DSM3959.     

Structure of the cell wall of Bacillus stearothermophiluys: mode of action of a thermophilic bacteriophage lytic enzyme

The mode of action of a bacteriophage lytic enzyme on cell walls of Bacillus stearothermophilus (NCA 1503-4R) has been investigated. The enzyme is an endopeptidase which catalyzes the hydrolysis of the l-alanyl-d-glutamyl linkage in peptide subunits of the cell wall peptidoglycan. Preliminary studies on the soluble components in lytic cell wall digests indicate that the glycan moiety is composed of alternating glucosamine and muramic acid; one half of the muramic acid residues contain the tripeptide, l-alanyl-d-glutamyldiaminopimelic acid, and the remaining residues contain the tetrapeptide, l-alanyl-d-glutamyldiaminopimeyl-d-alanine. Almost one half of the peptide subunits are involved in cross-linkages of chemotype I. A structure for the cell wall peptidoglycan is proposed in the light of these findings.     

A Novel Alginate Lyase with High Activity on Acetylated Alginate of Pseudomonas aeruginosa FRD1 from Pseudomonas sp. QD03

Summary To exploit alginate lyase which could degrade bacterial alginates, degenerate PCR and long range-inverse PCR (LR-IPCR) were used to isolate alginate lyase genes from soil bacteria. Gene algL, an alginate lyase-encoding gene from Pseudomonas sp. QD03 was cloned, and it was composed of a 1122 bp open reading frame (ORF) encoding 373 amino acid residues with the calculated molecular mass of 42.2 kDa. The deduced protein had a potential N-terminal signal peptide of 20 amino acid residues that was consistent with its proposed periplasmic location. Gene algL was expressed in pET24a (+)/E. coli BL21 (DE3) system. The recombinant AlgL was purified to electrophoretic homogeneity using affinity chromatography. The molecular weight of AlgL was estimated to be 42.8 kDa by SDS-PAGE. AlgL exhibited maximal activity at pH 7.5 and 37 °C. Na⁺, K⁺, Ca²⁺ and Ba²⁺ significantly enhanced the activity of AlgL. AlgL could degrade alginate and mannuronate blocks, but hardly degrade guluronate blocks. In particular, AlgL could degrade acetylated alginate of Pseudomonas aeruginosa FRD1 (approximately 0.54 mol of O-acetyl group per mol of alginate). It might be possible to use alginate lyase AlgL as an adjuvant therapeutic medicine for the treatment of disease associated with P. aeruginosa infection.     

Heparin/Heparan Sulfate 6-O-Sulfatase from Flavobacterium heparinum: INTEGRATED STRUCTURAL AND BIOCHEMICAL INVESTIGATION OF ENZYME ACTIVE SITE AND SUBSTRATE SPECIFICITY*

Heparin and heparan sulfate glycosaminoglycans (HSGAGs) comprise a chemically heterogeneous class of sulfated polysaccharides. The development of structure-activity relationships for this class of polysaccharides requires the identification and characterization of degrading enzymes with defined substrate specificity and enzymatic activity. Toward this end, we report here the molecular cloning and extensive structure-function analysis of a 6-O-sulfatase from the Gram-negative bacterium Flavobacterium heparinum. In addition, we report the recombinant expression of this enzyme in Escherichia coli in a soluble, active form and identify it as a specific HSGAG sulfatase. We further define the mechanism of action of the enzyme through biochemical and structural studies. Through the use of defined substrates, we investigate the kinetic properties of the enzyme. This analysis was complemented by homology-based molecular modeling studies that sought to rationalize the substrate specificity of the enzyme and mode of action through an analysis of the active-site topology of the enzyme including identifying key enzyme-substrate interactions and assigning key amino acids within the active site of the enzyme. Taken together, our structural and biochemical studies indicate that 6-O-sulfatase is a predominantly exolytic enzyme that specifically acts on N-sulfated or N-acetylated 6-O-sulfated glucosamines present at the non-reducing end of HSGAG oligosaccharide substrates. This requirement for the N-acetyl or N-sulfo groups on the glucosamine substrate can be explained through eliciting favorable interactions with key residues within the active site of the enzyme. These findings provide a framework that enables the use of 6-O-sulfatase as a tool for HSGAG structure-activity studies as well as expand our biochemical and structural understanding of this important class of enzymes.     

Studies on Plant Growth-regulating Activities of Anisomycin and Toyocamycin

A new enzyme, 2-methylisocitrate dehydratase, isolated from Yallowia lipolytica, functioning in the methylcitric acid cycle for propionate metabolism, had a pI of 4.4 and a M_r of 69,500. The enzyme was composed of 624 residues of amino acids per molecule. No cofactor was required for full enzyme activity. The enzyme was competitively inhibited by threo-D_s-isocitrate (K_i =68mM), but not by any other tested metabolites. The enzyme was weakly inhibited by some thiol reagents, but not by any metal-chelating reagents, differing from aconitase, which dehydrates 2-methylisocitrate. This difference between the enzymes made it possible to estimate the activity of the new enzyme even in crude cell-free extracts. The enzyme was constitutively synthesized, but had no regulatory function in the methylcitric acid cycle. The enzyme was supposed to have evolutionarily developed from a hypothetical and prototypical isocitrate dehydratase.     

Immunochemical studies of isolated human brain ganglioside components

Abstract— Gangliosides G₁ to G₅ were isolated from human brain by means of TLC and tested with respect to their specificity to antisera against normal brain and Tay-Sachs brain gangliosides by agar double diffusion analysis. Gangliosides G₂ and G₄ gave precipitation reactions with antisera to normal human gangliosides (NHG) while only ganglioside G₆ reacted with antisera to Tay-Sachs gangliosides (TSG). Additional specificity information was also obtained by use of the enzyme neuraminidase for the removal of specific sialic acid (NANA) residues. It was concluded from these data that the specificity of the anti-NHG antibodies is determined by the presence of a galactose (β1, 3) N-acetyl galactos-amine–while that of anti-TSG antibodies is due to a N-acetyl galactosamine (β1, 4) galactose-end sequence. By means of natural compounds of known structure it was found that both the sequence of carbohydrate residues and position of NANA residues in the molecule played a critical role in the formation of precipitation bands with NHG-antisera. This information was utilized to distinguish one isomeric form of disialoganglioside from another, i.e. G₂ from G₃ and to confirm the structure of the trisialoganglioside, G₁. The immunochemical method appears to be a useful one for elucidating structural differences in ganglioside molecules.     

The complete amino acid sequences of four globins from the land leech Haemadipsa zeylanica var. japonica

The amino acid sequences of four globins from the land leech, Haemadipsa zeylanica var. japonica, were determined using nucleotide sequencing and protein sequencing. The mature globin-molecules were composed of 146 amino acid residues for M-1 globin, 156 for M-2 globin, 143 for D-1 globin, and 149 for D-2 globin. Alignment of the four kinds of globins by Clustal X revealed 22 invariant amino acids. The four globins were 26–33% identical. A striking feature of amino acid alteration was: the replacement of the E7 distal-His of D-1 globin by phenylalanine because histidine is conserved among the rest of the globins of H. zeylanica, those of other representative species (Lumbricus and Tylorrhynchus) of Annelida and most other hemoglobins. A phylogenetic tree constructed of 18 globin structures including two species of leeches, H. zeylanica (a land leech) and Macrobdella decora (a freshwater leech), T. heterochaetus (a representative species of polychaetes), L. terrestris (a representative species of oligochaetes), and human α and β globins strongly indicated that the leech globins first separated from globin lineage of annelids.     

Biocatalytic modification of polyethylene terephthalate fibres by esterases from actinomycete isolates

The modification of polyethylene terephthalate (PET) fibres by extracellular enzymes produced by actinomycetes was investigated. Cultivation of isolates in media containing PET yarn and suberin, a plant polyester composed of aliphatic and aromatic moieties, induced the production of p-nitrophenyl butyrate hydrolyzing enzymes. Incubation of enzyme preparations from the isolates M5, M9 and Thermomonospora fusca KW3b with PET yarn resulted in an increase in the absorbance of the reaction mixtures at 240 nm indicating the release of terephthalic acid or its esters catalyzed by the enzymes. The results of dyeing of enzyme-treated PET fabrics with a reactive dye (CI Reactive Red 2) indicated an increase in hydroxyl groups at the fibre surfaces as a result of the enzyme treatment.     

Demonstration of a new amidase acting on glycopeptides

An enzyme preparation from almond emulsin cleaved the peptide-carbohydrate linkage of stem bromelain glycopeptide, Asn-Asn (oligosaccharide)-Glu-Ser-Ser. The resulting products were determined to be an intact peptide, Asn-$\text{Asp}$-Glu-Ser-Ser, and an intact oligosaccharide unit with two moles of N-acetylglucosamine. So far as tested the enzyme hydrolyzed glycopeptides with 3 to 10 amino acids, while both asparagine-oligosaccharide from ovalbumin and Asn-GlcNAc were not. Thus, the enzyme is a new amidase capable of hydrolyzing aspartylglycosylamine linkage in glycopeptides with multiple amino acid residues.     

Replacement of Methionine 208 in a Truncated <Emphasis Type="Italic">Bacillus</Emphasis> sp. TS-23 α-Amylase with Oxidation-Resistant Leucine Enhances Its Resistance to Hydrogen Peroxide

The methionine residues at positions 17, 104, 208, 214, 292, 315, 324, and 446 in the primary amino acid sequence of a truncated Bacillus sp. TS-23 α-amylase (His₆-tagged BLAΔNC) was changed to oxidative-resistant leucine by site-directed mutagenesis. The mutant enzymes with an apparent molecular mass of approximately 54 kDa were overexpressed in recombinant Escherichia coli. The specific activity for Met315Leu and Met446Leu was decreased by more than 76%, while Met17Leu, Met104Leu, Met208Leu, Met214Leu, Met292Leu, and Met324Leu showed 247, 128, 37, 260, 232, and 241%, respectively, higher activity than the wild-type enzyme. In comparison with wild-type enzyme, a lower K _m value was observed for all mutant enzymes. The 3.2- and 4.5-fold increases in the catalytic efficiency (k _cat/K _m) for Met208Leu and Met324Leu, respectively, were partly contributed by a 68% and 38% decrease in K _m values. Wild-type enzyme was sensitive to chemical oxidation, but Met208Leu was stable even in the presence of 500 mM H₂O₂. Except for Met214Leu, which was quite sensitive to H₂O₂, the other mutants showed a profile of oxidative inactivation similar to that of the wild-type enzyme. These observations indicate that the oxidative stability of His₆-tagged BLAΔNC can be improved by replacement of the critical methionine residue with leucine. Received: 12 April 2002 / Accepted: 8 June 2002     

Chemical Studies on the Cell Walls of Leptospira biflexa Strain Urawa and Treponema pallidum Strain Reiter

The preparation and chemical poperties of the cell walls of Leptospira biflexa Urawa and Treponema pallidum Reiter are described. Both cell walls are composed mainly of polysaccharides and peptidoglycans. The data of chemical analysis indicate that the cell wall of L. biflexa Urawa contains rhamnose, arabinose, xylose, mannose, galactose, glucose and unidentified sugars as neutral sugars, and alanine, glutamic acid, α,ε-diaminopimelic acid, glucosamine and muramic acid as major amino acids and amino sugars. As major chemical constituents of the cell wall of T. pallidum Reiter, rhamnose, arabinose, xylose, mannose, galactose, glucose, alanine, glutamic acid, ornithine, glycine, glucosamine and muramic acid have been detected. The chemical properties of protein and polysaccharide fractions prepared from the cells of T. pallidum Reiter were also partially examined.     

Structure‐based replacement of methionine residues at the catalytic domains with serine significantly improves the oxidative stability of alkaline amylase from alkaliphilic Alkalimonas amylolytica

The alkaline amylase requires high resistance towards chemical oxidation for use in the detergent and textile industries. This work aims to improve the oxidative stability of alkaline amylase from alkaliphilic Alkalimonas amylolytica by site‐directed mutagenesis based on the enzyme structure model. Five mutants were created by individually replacing methionine at positions 145, 214, 229, 247, and 317 in the amino acid sequence of alkaline amylase with oxidative‐resistant serine. The pH stability of the mutant enzymes was almost the same as that of the wild‐type (WT) enzyme (pH 7.0–11.0). The stable temperature range of the mutant enzymes M145S and M247S decreased from <50°C of the WT to <40°C, while the thermal stability of the other three mutant enzymes (M214S, M229S, and M317S) was almost the same as that of the WT enzyme. The catalytic efficiency (k_cat/K_m) of all the mutant enzymes decreased when compared to WT enzyme. The mutant enzymes showed increased activity in the presence of surfactants Tween‐60 and sodium dodecyl sulfate. When incubated with 500 mM H₂O₂ at 35°C for 5 h, the WT enzyme retained only 13.3% of its original activity, while the mutant enzymes M145S, M214S, M229S, M247S, and M317S retained 55.6, 70.2, 54.2, 62.5, and 46.4% of the original activities, respectively. The results indicated that the substitution of methionine residues at the catalytic domains with oxidative‐resistant serine can significantly improve the oxidative stability of alkaline amylase. This work provides an effective strategy to improve the oxidative stability of amylase, and the high oxidation resistance of the mutant enzymes shows their potential applications in the detergent and textile industries. © 2012 American Institute of Chemical Engineers Biotechnol. Prog., 2012